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Old 01-19-2013, 01:01 PM   #1
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Brake wire continuity?

I recently installed new brake wire on my dual axle trailer. My Tekonsha controller says NC so I'm attempting to troubleshoot. When I connect a multimeter to the leads of my new trailer brake wire it shows continuity with no resistance. How do I interpret this result and what is the next step?
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Old 01-19-2013, 02:29 PM   #2
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Are you checking from the magnets to the pin on the plug? The complete run of the brake wires?
If that checks OK, I would check plug, both the male and female ends.
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Old 01-19-2013, 03:46 PM   #3
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Thanks for the reply. I was checking the complete run of the brake wires. Is it supposed to have continuity? Just now I disconnected all four brakes and checked my new brake wires for continuity between the white and black and there is none. I applied 12 volts to all four wheels, one at a time and could hear a faint click. Maybe there isn't anything wrong with my trailer wiring...just trying to rule it out. If i run a jumper wire from my trucks blue wire to the white ground I expected the NC on my controller to change to C but it didn't. Going to be 15 below zero tonight and would sure love to figure this out.

I am getting a voltage reading on the blue wire when depressing brake.
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Old 01-20-2013, 02:26 PM   #4
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After more testing I am getting 12 volts out of the blue wire at my brake controller while activated the manual brake lever and only 1.5 volts at the back of truck before the trailer connector. So I'll check the blue wire under my truck for loose connections. I still want to know if the trailer brake wire should have continuity. It should right? It's a simple circuit where the voltage travels from ground to positive? If one of my magnets had a short to ground would it still show continuity on my meter?
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Old 01-20-2013, 03:38 PM   #5
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The best way to check the trailer brakes is to measure the current flow to them. On your 7 way connector, find the terminal which goes to the brakes. Then find the terminal with + 12 volts on it. Connect your ammeter between those two terminals. You should have a reading of between 3 and 3.5 amps for each trailer brake magnet, that is in the range of 12 amps for all four working brakes. It is not uncommon, when doing this test, to find a current of around 9 amps (three brakes working) or 6 amps (two brakes working). I had the horror once on my own trailer of only finding a current draw of 3 amps. Three of the 4 brake wires were corroded and the brakes were not working on them.

So, continunity of the brake wire really does not tell much of the story. Measure the current flow and at least if it is in the 3 amp range per wheel, the electrical part of the brakes should be working.
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Old 01-20-2013, 03:44 PM   #6
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After more testing I am getting 12 volts out of the blue wire at my brake controller while activated the manual brake lever and only 1.5 volts at the back of truck before the trailer connector. So I'll check the blue wire under my truck for loose connections. I still want to know if the trailer brake wire should have continuity. It should right? It's a simple circuit where the voltage travels from ground to positive? If one of my magnets had a short to ground would it still show continuity on my meter?
Any trailer brakes that I have messed with have had a few ohms when measured to ground. I'm not sure how many ohms, but I do remember that I found the value with a search on the Internet.

Ken
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Old 01-20-2013, 04:20 PM   #7
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The best way to check the trailer brakes is to measure the current flow to them. On your 7 way connector, find the terminal which goes to the brakes. Then find the terminal with + 12 volts on it. Connect your ammeter between those two terminals. You should have a reading of between 3 and 3.5 amps for each trailer brake magnet, that is in the range of 12 amps for all four working brakes. It is not uncommon, when doing this test, to find a current of around 9 amps (three brakes working) or 6 amps (two brakes working). I had the horror once on my own trailer of only finding a current draw of 3 amps. Three of the 4 brake wires were corroded and the brakes were not working on them.

So, continunity of the brake wire really does not tell much of the story. Measure the current flow and at least if it is in the 3 amp range per wheel, the electrical part of the brakes should be working.
Cool, thanks. I will check the amps to the brakes. I did find a loose connection under the truck on the blue wire and I'm going to repair it right now. I'm wondering if that was the reason NC was showing on the controller. I guess I'll find out.
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Old 01-20-2013, 05:12 PM   #8
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Cool, thanks. I will check the amps to the brakes. I did find a loose connection under the truck on the blue wire and I'm going to repair it right now. I'm wondering if that was the reason NC was showing on the controller. I guess I'll find out.
I will be amazed if that doesn't fix the problem.

Ken
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Old 01-20-2013, 05:27 PM   #9
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The resistance of each magnet is about 3 ohms so four magnets in parallel would be less than 1 ohm, or essentially no resistance. Magnet current is on the order of 2.5 to 3 amps for a total of 10 to 12 amps for all 4 wheels. As the magnets heat the current will drop

If you are only seeing a couple volts at the back of the truck, you either have a high resistance on the truck end or as happened to me once, someone had bumped the adjustment knob and the controller was turned way down
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Old 01-20-2013, 09:36 PM   #10
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The resistance of each magnet is about 3 ohms so four magnets in parallel would be less than 1 ohm, or essentially no resistance. Magnet current is on the order of 2.5 to 3 amps for a total of 10 to 12 amps for all 4 wheels. As the magnets heat the current will drop

If you are only seeing a couple volts at the back of the truck, you either have a high resistance on the truck end or as happened to me once, someone had bumped the adjustment knob and the controller was turned way down
Ah, that would explain the very little resistance I got because I did wire the four magnets in parallel. That's great to know about that amp test.

My problem was indeed my splice into the blue wire under the truck. After I fixed it I hooked up only one brake and my controller changed from a constant NC to flashing between NC and C. I figured I still had a short somewhere but then realized the controller might be looking for at least two brakes, so after hooking a second brake up I'm now getting a constant C. Thanks for all the great answers.

Cheers.

Eric
(in Wisconsin trying to get to Oregon coast.)
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